Multicast scheme with subgroups over heterogeneous cellular network

Wireless multimedia traffic has increased considerably in recent years, which puts forward higher demand on the capacity of existing network. Multicast, as a transmission strategy with high spectral efficiency, has not been widely studied in heterogeneous cellular network (HetNet). Meanwhile, in order to overcome the shortcoming of conventional multicast scheme (CMS) that the throughput of multicast group is constrained by the user with lowest data rate, we propose a multicast scheme with subgroups over HetNet to effectively improve the system throughput. We formulate an expression of system throughput of the proposed multicast scheme with subcarrier and power constraints and maximize it by optimizing subgroups configuration. It can be proved to be a NP-hard combinatorial problem, then we decouple it into three subproblems, namely, user association (UA), subgroup formation (SF) and resource allocation (RA). In UA, we present a traffic-oriented access method based on reference signal receiving power (RSRP). In SF, the associated users are divided into several subgroups according to their channel state information (CSI) and the users in one subgroup are served with appropriate rate determinated by the CSI level of the subgroup. In RA, Round-Robin schedule and Equal Power schedule are adopted for subcarrier allocation and power allocation respectively. Simulation results show that the system throughput is significantly improved by using our scheme.